From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C265C4320A for ; Tue, 17 Aug 2021 09:13:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F31F060FD8 for ; Tue, 17 Aug 2021 09:13:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235490AbhHQJOE (ORCPT ); Tue, 17 Aug 2021 05:14:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39908 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234347AbhHQJOD (ORCPT ); Tue, 17 Aug 2021 05:14:03 -0400 Received: from mail-pj1-x102e.google.com (mail-pj1-x102e.google.com [IPv6:2607:f8b0:4864:20::102e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6DF38C061764; Tue, 17 Aug 2021 02:13:30 -0700 (PDT) Received: by mail-pj1-x102e.google.com with SMTP id fa24-20020a17090af0d8b0290178bfa69d97so5410934pjb.0; Tue, 17 Aug 2021 02:13:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:message-id:date:user-agent:mime-version :content-language:content-transfer-encoding; bh=7hFl+lvECuO7AZrUUDXWnuHbyid4dTyMDCfojPCaIqo=; b=HbAwPBVxqYVBNSIWFUVtrs0IMzcWdevND/Bs5whRGJRR3xcQUwPv8ASMjr9F5vBtKs UVF269FKV2jKsog2X0w9D46iqKy29PT4sdgDVUsTau49IddPeAcuLDRHDr15uPf0t9EL 6Xvhh/U2NQStRmd4VYneToiEWY19ADO/i/1Gyn3I/LbgirDY3AJaKScapVq6Ie5xiryz BZavh8YDNJS6OyyEoYOgsNQDFW3oxspgCbVOOogXCRPkZPmBzRSnsYl0GiIrnPiJN9Tu WTlJ9RvtCbaY66mhSa1YYXnbg3LV4TD0QP+jx9n8QIS8tC/G0sGS5mZluZDg3+GVT7gs RLhA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:message-id:date:user-agent :mime-version:content-language:content-transfer-encoding; bh=7hFl+lvECuO7AZrUUDXWnuHbyid4dTyMDCfojPCaIqo=; b=qwpS5QXVHgoP3lCk6fO63if/PU38dScytagqJyjmnXsllmyyIaXWfN9s4sCHoX5U58 wA9bnnZbLCcqk5r1GgfVrOobQ2A6M3mbq8+LV3ZPlzNrkWjwfuNryj+8GPq4M4bucHy5 Yf1l5QXfFF7D9OjEEDDyEiwfdDldV9+Yv7DoS6qx4n9WH6wE3g4MtszZY4pEWVp83E3T ujFhn7z/JBRwmlYtUUhQX5YDj1NZnTbNgKmRKRIRYYkLeD+BzQzB5003GX9cMX/ENc4r MolVPANsLnJsci6Da5DV5lXQRQTY+FYuyK0V3bJpnAOX3IgUHD9OEDepDDTMUc9cCope PUbQ== X-Gm-Message-State: AOAM533gaGRhDsXwRQ3f0bhgEWWeI1DbLJZ5tFB26kqn18Es8mB0BJ0x wFRBSFNQXFVfCCWDjb2wohA= X-Google-Smtp-Source: ABdhPJxHI1dM8zK2COH1XPjzlYAwHAHgWtNEqcIr/Bsks62txFI2scVFQWlvqty7C3PvXy8uJLiEhg== X-Received: by 2002:a17:90a:384b:: with SMTP id l11mr2699892pjf.208.1629191609882; Tue, 17 Aug 2021 02:13:29 -0700 (PDT) Received: from [10.211.55.3] ([202.78.233.119]) by smtp.gmail.com with ESMTPSA id n22sm1853892pff.57.2021.08.17.02.13.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Aug 2021 02:13:28 -0700 (PDT) From: Saubhik Mukherjee To: isdn@linux-pingi.de, gregkh@linuxfoundation.org, jirislaby@kernel.org, dsterba@suse.com, jcmvbkbc@gmail.com, johannes@sipsolutions.net, kuba@kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, andrianov@ispras.ru Subject: [question] potential race between capinc_tty_init & capi_release Message-ID: Date: Tue, 17 Aug 2021 14:43:22 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In drivers/isdn/capi/capi.c, based on the output of a static analysis tool, we found the possibility of the following race condition: In capi_init, register_chrdev registers file operations callbacks, capi_fops. Then capinc_tty_init is executed. Simultaneously the following chain of calls can occur (after a successful capi_open call). capi_release -> capincci_free -> capincci_free_minor -> capiminor_free -> tty_unregister_device tty_unregister_device reads capinc_tty_driver, which might not have been initialized at this point. So, we have a race between capi_release and capinc_tty_init. If this is a possible race scenario, maybe moving register_chrdev after capinc_tty_init could fix it. But I am not sure if this will break something else. Please let me know if this is a potential race and can be fixed as mentioned. Since this is based on a static analysis tool, this is not tested.